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All IPCC definitions taken from Climate Change 2007: The Physical Science Basis. Working Group I Contribution to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change, Annex I, Glossary, pp. 941-954. Cambridge University Press.

What is the link between hurricanes and global warming?

What the science says...

There is increasing evidence that hurricanes are getting stronger due to global warming.

Climate Myth...

Hurricanes aren't linked to global warming
“According to the National Hurricane Center, storms are no more intense or frequent worldwide than they have been since 1850. […] Constant 24-7 media coverage of every significant storm worldwide just makes it seem that way.” (Paul Bedard)

The current research into the effects of climate change on tropical storms demonstrates not only the virtues and transparency of the scientific method at work, but rebuts the frequent suggestion that scientists fit their findings to a pre-determined agenda in support of climate change. In the case of storm frequency, there is no consensus and reputable scientists have two diametrically opposed theories about increasing frequencies of such events.

The background to these enquiries stems from a simple observation: extra heat in the air or the oceans is a form of energy, and storms are driven by such energy. What we do not know is whether we might see more storms as a result of extra energy or, as other researchers believe, the storms may grow more intense, but the number might actually diminish.

What do the records show? According to the Pew Centre, “Globally, there is an average of about 90 tropical storms a year”. The IPCC AR4 report (2007) says regarding global tropical storms: "There is no clear trend in the annual numbers [i.e. frequency] of tropical cyclones."

But this graph, also from the Pew Centre, shows a 40% increase in North Atlantic tropical storms over the historic maximum of the mid-1950, which at the time was considered extreme:

But while the numbers are not contested, their significance most certainly is. Another study considered how this information was being collected, and research suggested that the increase in reported storms was due to improved monitoring rather than more storms actually taking place.

And to cap it off, two recent peer-reviewed studies completely contradict each other. One paper predicts considerably more storms due to global warming. Another paper suggests the exact opposite – that there will be fewer storms in the future.

What can we conclude from these studies? About hurricane frequency – not much; the jury is out, as they say. About climate change, we can say that these differing approaches are the very stuff of good science, and the science clearly isn’t settled! It is also obvious that researchers are not shying away from refuting associations with climate change, so we can assume they don’t think their funding or salaries are jeopardised by research they believe fails to support the case for AGW. The scientific method is alive and well.

Never mind the frequency, feel the width

So far, all we’ve managed is to document here is what we don’t know for sure yet. But we do know there is extra energy in the system now, so could it have any other effects on tropical storms? Here, the science is far less equivocal, and there is a broad consensus that storms are increasing in strength, or severity. This attribute, called the Power Dissipation Index, measures the duration and intensity (wind speed) of storms, and research has found that since the mid-1970s, there has been an increase in the energy of storms.

Recent research has shown that we are experiencing more storms with higher wind speeds, and these storms will be more destructive, last longer and make landfall more frequently than in the past. Because this phenomenon is strongly associated with sea surface temperatures, it is reasonable to suggest a strong probability that the increase in storm intensity and climate change are linked.

Comments

"It's important to remember that hurricane activity is just one possible side-effect of global warming. While the empirical evidence linking global warming and hurricane intensity seems robust, it has no bearing on the central question of whether human CO2 emissions are causing global warming."

True, but if human CO2 emissions causing global warming do not have damaging consequences, such as increased storm activity, the 'central question' is no longer central, is it?

Response: If the only consequence of global warming was increased hurricane activity, then you'd have a point. However, they are the tip of the iceberg (pardon the pun). See positives and negatives of global warming for a more comprehensive list.

Your list of potential catastrophes makes interesting reading. But there are no citations, so I wonder how many of these items are speculations and how many have any scientific backing to them. Presumably if the global temperature dropped 2C then we could construct an equally long list of potential catastrophes. It seems that the implications of all this is that somehow, miraculously, the current average global temperature must be perfect.

"Titled "Effect of Remote Sea Surface Temperature Change on Tropical
Cyclone Potential Intensity," their study found that long-term changes
in potential intensity are more closely related to the regional
pattern of warming than to local ocean temperature change. Regions
that warm more than the tropical average are characterized by
increased potential intensity, and vice versa. "A surprising result is
that the current potential intensity for Atlantic hurricanes is about
average, despite the record high temperatures of the Atlantic Ocean
over the past decade." Soden said. "This is due to the compensating
warmth in other ocean basins."

"As we try to understand the future changes in hurricane intensity, we must look beyond changes in Atlantic Ocean temperature. If the Atlantic warms more slowly than the rest of the tropical oceans, we
would expect a decrease in the upper limit on hurricane intensity,"
Vecchi added. "This is an interesting piece of the puzzle."
- A. McIntire

..........Landsea et al, 2009 (From NYT Aug12, 2009)
The researchers studied storms that played themselves out at sea, either in a day or two or over a longer period, from 1878 to 2008. By the late 19th century, they estimated meterologists missed perhaps two of the larger storms each year, and by the 1950s they were picking up on average all but one each year.
Yet the researchers estimate that a century ago, as many as 80 percent of short-lived storms came and went without ever being officially noticed.
Over all, they conclude, storm counts have not changed in the last century.

..........Mann et al, 2009 (Ditto)
...used a mathematical model of hurricane activity and measurements of sediment to estimate how often major storms struck the Gulf and Atlantic Coasts of the United States in the last 1500 years.
...the researchers worked with sediment samples from Puerto Rico, the Gulf Coast and the Atlantic Coast from Florida to New England.

Although current numbers are relatively high, they say, both analytical methods suggest that a period of high storm frequency, possibly even higher than today's, began in the year 900 and lasted until 1200 or so.

In a new study, Clemson University researchers have concluded that the number of hurricanes and tropical storms in the Atlantic Basin is increasing, but there is no evidence that their individual strengths are any greater than storms of the past or that the chances of a U.S. strike are up.
...studied changes in the tropical cycle record in the North Atlantic between 1851 and 2008.
"This is a hot button issue in the argument for global warming," said Lund. "Climatologists reporting to the U.S. Senate as recently as this summer testified to the exact opposite of what we find. Many researchers have maintained that warming waters of the Atlantic are increasing the strength of these storms. We do not see evidence for this at all, however we do find that the number of storms has recently increased."
The study represents one of the first rigorous statistical assessments of the issue with uncertainty margins calculated in...
While the study did conclude that more storms are being documented, researchers found no evidence of recent increases in U.S. landfall strike probability of the strongest hurricanes. Lund notes that "because these types of storms are so uncommon, it will take many years of data to reliably assess this issue."

...while water temperature is the most important factor in tropical cyclone dynamics, many other environmental factors affect these storms. These include: the deep warm water; moisture availibility; weak wind shear; a source of rotation, and no land interaction/landfall. Only when all these factors exist can a hurricane reach its maximum potential intensity for a given water temperature. In fact, few hurricanes reach their potential because some inhibiting factor exists. Furthermore, global warming could enhance some negative influences regionally; an ensemble of 18 global climate models show that wind shear and dry air will increase in the Atlantic, while in contrast the opposite occurs in the west Pacific where environmental factors favor more hurricanes. Therefore, anthropogenic warmer oceans do not necessarily correlate to increased tropical cyclone activity or stronger hurricanes globally. Climate models give mixed results on whether the average storm intensities will change, but most show evidence for some increase in intensity.
Pat Fitzpatrick, Hurricanes and Climate...~2007

One inhibiting factor is the El Nino, a body of relatively warm equatorial water in the eastern Pacific. Absent for the past few years, it is expected to bring weak to moderately warm water to the South American west coast. A characteristic of El Nino is westerly winds in the upper troposphere that act to shear the tops off Atlantic easterly waves coming off the African Coast, preventing them from growing into named storms or hurricanes...
However, this (weak to moderate) El Nino will fall well short of the one that occurred in 2007, limiting the season's total named storms to seven.
From William Gray's 2001 hurricane forecast

Working in a strategically located lagoon off Puerto Rico, Donelly and Woodruff compiled the long record (cores, 2007) of strong hurricanes in the Atlantic region. The 5,000 year record identified two factors that appeared to heighten Atlantic activity: weak El Ninos in the tropical Pacific and strong monsoons in West Africa.
Scientists have established that strong El Ninos can stunt hurricane activity by causing strong high-altitude winds that inhibit hurricane formation.
Other reseaqrchers have identified that storms over western Africa generate atmospheric waves that move into the Atlantic and provide "seedlings" for hurricane development...
Oceanus Feb 13, 2009

The formation of Atlantic hurricanes also appears to be strongly influenced by Saharan dust. The dust from the Sahara tracks westwards into the ocean and causes local cooling, depressing the temp. below thresholds needed for hurricanes to form.

ntrs.nasa.gov/archive/nasa/casi.../20080039568_2008038939.pdf - summarises the work by Lau & Kim.

Glad the consensus has determined hurricane frequency should be retired to the ash heap of arguments. So how did this one slip through the consensus?

----
Global warming is causing more frequent hurricanes in the North Atlantic and Gulf of Mexico, according to a study from the National Center for Atmospheric Research.

The increased frequency of tropical cyclones ``is largely a response'' to a 1 degree Celsius rise in sea water temperatures since 1905 that was caused by greenhouse gases, the study found. Since 1995, the North Atlantic has experienced an average of 15 tropical storms a year, of which eight became strong enough to be called hurricanes. That compares with 10 tropical storms and five hurricanes per year from 1930 to 1994, the report says.

``There is an 80 percent chance that the majority of the current increases have been impacted by global warming,'' said Greg Holland, director of the research center in Boulder, Colorado, and co-author of the study. ``The bad news is that we've gone up in numbers overall, and in the proportion of major hurricanes as well.''

Sorry guys. Neither hurricane frequency nor intensity is related to AGW. If anything, there is a slight century scale decrease in hurricane activity over the Atlantic (with huge swings up & down). Click on image for explanation

One thing is sure. To choose 1972 for a starting point of the analysis (as in Fig. 2 above) is utterly misleading.

Given that we can date the current global warming period starts in around 1975 it's a valid hypotheis to ask whether that has an influence on hurricane frequency and intensity.

In fact, despite some suggestion that both have increased since the early 1970s, it seems from the data that the effect size is small, and because hurricanes are a complex phenomenon, it will take quite a while to have enough data to determine the relationship. Pretending that this hypothesis is somehow disproven is massively overstating your case, and shows that the work you do on this topic is tainted by your preconceptions.

#10kdkd at 20:08 PM on 19 August, 2010despite some suggestion that both have increased since the early 1970s

Of course they did. However, if one is trying to do valid climate science, the first question to ask is why hurricane intensity has dropped dramatically between 1959 and 1972?

Until we have an answer to that question, there is no point in making fancy theories about the partial recovery after 1990 which still have not reached the levels once seen during the 1940s. Not even those in the 1880s when temperature is supposed to be way lower than today.

#11: "why hurricane intensity has dropped dramatically between 1959 and 1972?"
The question is based on a still-questionable statistic of cumulative SSn by year.

There are many problems with this statistic. Is a year with 3 cat 2 storms 20% worse than a year with 1 cat 5? There are many residents of the Gulf Coast and Florida who would vehemently disagree. The SSn given is at landfall (so that Katrina is a cat 3); it was cat 5 just offshore when it was piling up the storm surge that destroyed lower New Orleans.

And why does the graph shown stop in 1995, when it is labeled as representing 1851-2009? Surely a trailing average could include those more recent (and more active) years.

'Dropped dramatically' seems to stem from the trend of -0.43 per century. Is there any statistical significance to such a small number? Especially when we routinely hear challenges to a temperature trend of 0.15 degC/decade, nearly 4x as large.

In terms of accumulated cyclone energy (ACE; the sum of the squares of the maximum wind speed at 6-h intervals for all tropical and subtropical cyclones with intensities of 34 kt or greater; Bell et al. 2000), the 2005 season had a record value of about 256% of the longterm (1944–2003) mean. The previous record was about 249% of the long-term mean set in 1950. [emphasis added]

So let's not claim that hurricane intensity is dropping over the long term.

Nope, again, that's a hypothesis (over an even shorter time time span than the early 70s to the present day where we have an increase). This hypothesis will be difficult to test due to low statistical power, and because it's unclear what should be measured to test it (or if the measurements are available).

Again you're overstating your case. In this example you appear to be cherry picking to suit your preconceptions.

I was playing around with some North Atlantic hurricane data and got a chart very similar to figure 1 above (except up through 2009 and without the 'major hurricanes' distinction) when something occurred to me.

How can Landsea make the 'better detection' argument when there is no evidence of a change in values when the detection methods changed? If you look at the 'tropical storms' section from the end of the 'ships with radio' period through 'aircraft', 'radar', and the start of 'satellite' tracking there is very little change... just some minor up/down variation. If Landsea's claim that storms were systematically missed by the older methodologies were true there should be one or more significant jumps in there. Instead, we see storm levels holding fairly steady until ~20 years into the satellite tracking era... and then climbing steadily for the 20 years since then.

Granted, the period of sharply increasing storm activity is fairly short and difficult to draw definitive conclusions from... but that doesn't change the fact that the data doesn't show any evidence of the measurement bias Landsea suggests is behind the increase.

Also note that there was an earlier increase in frequency up until leveling off around 1950... that corresponds to the early 20th century warming period and the leveling off to a period of more level temperatures... all within the 'ships with radios' measuring period. Again, it is a short timeframe, but again there seems to be a correlation to temperatures rather than measurement methodology.

All of these trends are present, but less distinct, on the 'hurricanes' and 'major hurricanes' subsets of the data as well. Obviously the temperature to storm/hurricane count correlation is not a perfect match... but there is NO correlation between the changing methodologies and increasing storm/hurricane count. Doesn't that invalidate Landsea's argument?

Recently I was talking to a skeptic I know in the USA (the same one I've mentioned here on other threads)and I was telling him about how the massive floods we're having in Australia are linked to climate change and this was his response:

"In another time your Green MP upon seeing an eclipse of the sun would have jumped upon a soap box and proclaimed, “Give me your money now or I shall blot out the sun again!” You can see how far we’ve come, today’s MP upon seeing a flood, says in effect, “give me power or there will be no one to protect you from the evil forces of greedy industrialists!” Ah, progress!

You should take heart though, after hurricane Katrina hit the U.S. Greens were coming out of the woodwork predicting a new era of increased severe hurricane activity caused by global warming. Not only has there not been another severe hurricane to hit the U.S. but all hurricane activity has dropped off precipitously. Of course the way is now clear for Greens to point out the “fact” that the unnatural drop-off in hurricane activity is an example of rampant global warming!

Four years ago, the area of California around L.A. was experiencing a drought. Greens were quick to point out that global warming was turning California into a desert and that California should brace itself for perpetual drought. Yes … currently, the rains in California have been so drastic that mudslides are what threaten humanity, not lack of water. Still Californians, who must be the holy grail for con-men the world over, rushed to pass laws aimed at curbing emission standards, ransacking their homes for anything of value to throw on the pile of wealth in hopes that the wizard will be pleased and the sun will not be blotted out again. And it goes without saying that the Greens have pointed out that the above average rainfall of the last two years in California is an example of the kind of “Global chaos” that we should come to expect from increased Co2 emisions.

Mankind is responsible for about .28% of all of the greenhouse gases in the atmosphere. If the entire U.S. stopped producing Co2 gas completely tomorrow the effect could not be measured yet here we have a Green in Aus passionate that Melbourne reduce its Co2 emissions so that floods will be prevented.

The fact that people are still threatening to blot out the sun unless they are paid off isn’t what’s surprising, the surprising thing, and the very sad thing, is that people are still lining up to give away their wealth and freedom to the latest Hucksters."

Chris, here's my suggestion FWIW. Preparation for storms is essential regardless of averages and predictions. Alt energy will work well with a smart grid. Arguing about whether "CAGW" is a religion doesn't advance science and most of his examples are red herrings, the science is not capricious or extreme. The article at the top of this thread is a good example of that.

I'm intrigued by the Hurricane story. If the atmosphere is getting warmer then one would expect tropical storms to increase in both frequency and intensity as there would be more energy in the system to power them, therefore one would expect more to become Hurricane force too, so overall average numbers should go up along with their average power.

I have decided to do my own research on this, and it hasn't been easy finding reasonably reliable data that goes back a decent amount of time. As it is I have found archive data from ships reports and later monitoring reports of Hurricanes from 1851 to 2010, this later data, from 1995 does indeed see a marked increase in both tropical storms, hurricanes and their relative energy, based on wind speeds, I appreciate that until the more modern era wind speed assumptions for such events have a degree of error in them..afterall people on a ship were a little busy to be doing too much science!

I'll be honest, I did not see any real rise or fall in the figures until I got to the 1990's, then both the number of events and the average wind speed has increased. I will plot this information into graphs and publish it for everyone to look at..but it will take a little while..I will also try to get some information, accurate, on how wind speeds were reported, if there has been a change to which tropical storms are recorded, such as a lowering of the minimum speed for recording purposes as this will allow a better understanding of the increase from 1995 on. If there has been no recording change, then the number has most definitely increased, as has the power of the events...and this would certainly imply that there is more energy in the system to power these storm, and that certainly indicates a rise in temperature over this period.

I will try to get it online in the next few days..as this intrigues me..

Response: Read the original post carefully. Notice that not all researchers agree with you that "one would expect tropical storms to increase in both frequency and intensity as there would be more energy in the system to power them." It's more complicated than that.

Why do you assume I did not read it? If you notice I used the word..assume..under normal circumstances when one puts more energy into a system, you get more energy out of it..I am not stating that either side of this comment is correct..If, and it is a big if, the atmosphere works the same as other systems in nature, then it is a reasonably conclusion to arrive at that by putting more energy into the system, one would expect more energy out, and in the case of tropical storm, one would expect more of them and likely with a higher energy level..but that is not necessarily the case. The only way to find out, or at least get a better handle on it is to go through all the available data that can be accepted as reasonably reliable and then put it into a useful and unbiased format. Then look at all other influences that may either positively or negatively impact any of that information...I am sure that, regardless of air and sea temperatures, there is far more going on to influence a tropical storm into becoming a Hurricane than we realise at this time..Like I said, this part of the discussion intrigues me...

"... or there's no connection whatsoever between temperature and storminess."

No connection whatsoever is a strong phrase in this context. From Jeff Masters:

Tomas' formation ties 2010 with 1995 and 1887 for 3rd place for most number of named storms in an Atlantic hurricane season. Only 2005 (28 named storms) and 1933 (21 named storms) were busier. ... The intensification of Shary and Tomas into hurricanes today brings the total number of hurricanes this season to twelve, tying 2010 with 1969 and 1887 for second place for most hurricanes in a season. The record is held by 2005 with fifteen hurricanes ...
-- emphasis added

But your 'scatterplot' is meaningful? Hardly. Let's stop throwing judgments around. Perhaps an appeal to actual science is in order.

Here's Elsner 2008: Atlantic tropical cyclones are getting stronger on average, with a 30-year trend that has been related to an increase in ocean temperatures over the Atlantic Ocean and elsewhere ...

Knutson et al 2008 report a different view:we assess, in our model system, the changes in large-scale climate that are projected to occur by the end of the twenty-first century by an ensemble of global climate models, and find that Atlantic hurricane and tropical storm frequencies are reduced. At the same time, near-storm rainfall rates increase substantially ...

What's worse? More frequent storms or stronger storms with heavier rainfall events? Check the residents of the US Gulf Coast or Queensland for their preferences.

What's to explain? Your own words, #23: "If anything, there's a weak ..." The 'if' and 'weak' loom large indeed when one looks at the graph in #23.

But here's how the folks who gather the Accumulated Cyclone Energy data forecast the 2010 storm season:
The lower caption states expected ACE range is mainly above 175% of median, which reflects the high likelihood of a very active season (also called hyperactive). Note that a 'high-activity era' started in 1995 and now the bars are red.

I don't think it does much good to your cause to cherry pick an old North Atlantic ACE forecast for 2010 when we are already well into 2011, so we have got facts. According to them, North Atlantic ACE was indeed somewhat above average, even if at the lower end of the forecast you have cited.

More importantly, we are talking about global warming here, not about some North Atlantic Warming. And global ACE for 2010 was way below average, close to an all time low.

Large-scale climate features strongly influenced this year’s hurricane activity, as they often do. This year, record warm Atlantic waters, combined with the favorable winds coming off Africa and weak wind shear aided by La Niña energized developing storms. The 2010 season continues the string of active hurricane seasons that began in 1995.

But short-term weather patterns dictate where storms actually travel and in many cases this season, that was away from the United States. The jet stream’s position contributed to warm and dry conditions in the eastern U.S. and acted as a barrier that kept many storms over open water. Also, because many storms formed in the extreme eastern Atlantic, they re-curved back out to sea without threatening land.

The alleged cherrypick of using just the Atlantic (a big cherry, that one) was initially your move. As we've said, this question isn't a settled one; no one even knows the proper metric to use.

"According to NOAA the 2010 Atlantic hurricane season, which ends tomorrow, was one of the busiest on record. In contrast, the eastern North Pacific season had the fewest storms on record since the satellite era began.

In the Atlantic Basin a total of 19 named storms formed – tied with 1887 and 1995 for third highest on record. Of those, 12 became hurricanes – tied with 1969 for second highest on record. Five of those reached major hurricane status of Category 3 or higher.

From Dr. Jeff Masters' blog:"This year's Accumulated Cyclone Energy (ACE) index was 163, putting it in 13th place for ACE since 1944. A "hyperactive" hurricane season is considered to have an ACE index of >175% of the median. According to Wikipedia, median ACE measured over the period 1951–2000 for the Atlantic basin was 87.5, so 2010 is a hyperactive year by that definition (183% of the median.)"

Professor Maue at FSU obtained an ACE of 170 for the N. Atlantic in 2010, the 11th highest since 1950, and highest since 2005.

Good idea. Their prediction in August 2010 for annual North Atlantic ACE was between 148×104 kt2 & 236 ×104 kt2. The actual figure is something like 163-170 (if we go with Dr. Jeff Masters or Dr. Ryan N. Maue). That's in the lower quarter of the forecast, i.e. close to the lower end of it. But the real insult is that the National Hurricane Center of the U.S. of A. still does not have the facts for 2010, although the year is somewhat over.

The alleged cherrypick of using just the Atlantic (a big cherry, that one) was initially your move.

Sit down please, you have not listened. That one is accumulated intensity of hurricanes making landfall in the US since 1863. It just puts things into historical perspective and the US was chosen only because old hurricanes there are well documented. It has nothing to do with North Atlantic ACE (as 2010 clearly shows).

Here and now we are talking about the satellite era, for which we have pretty accurate global estimate for ACE including tropical storms that do not make landfall anywhere.

And no, the North Atlantic is not a big cherry, it's less than 8% of the surface of the globe. As I have said, global ACE for 2010 was low. My scatterplot above is also for global ACE and as such, it is meaningful indeed.

BP:
Do I understand you to claim that since the Atlantic ACE was at the lower end of an extraordinarily high prediction that means it was low? Albatross has cited data that show the Atlantic ACE was high in 2010 and you need to admit that.

Your claiming that we should rely on a tiny percentage of the data (USA landfalling hurricanes) instead of the entire record is unscientific. The remainder of the hurricane record is not as bad as you claim. You need to drop this claim as it hurts what is left of your reputation.

"My scatterplot above is also for global ACE and as such, it is meaningful indeed."

Well, you are entitled to your opinion, no matter how misguided it may be and no matter how unscientific. I can try and hook you up with Christopher Monckton if you like...

As I'm sure you know, TCs are primarily a tropical phenomenon except on those occasions when they undergo extra-tropical transition. So your scatterplot might have been more "meaningful" or convincing had you looked at OHC (or SSTs) for the tropics, instead of lower-tropospheric temperatures for the globe (from a group/product with a less than reputable history).

#29: "the real insult is that the National Hurricane Center ... still does not have the facts for 2010"

Only can be considered an insult if true. As Albatross notes in #32, here are the facts, as of 29 Nov 2010:According to NOAA the 2010 Atlantic hurricane season, which ends tomorrow, was one of the busiest on record. In contrast, the eastern North Pacific season had the fewest storms on record since the satellite era began.

In the Atlantic Basin a total of 19 named storms formed – tied with 1887 and 1995 for third highest on record. Of those, 12 became hurricanes – tied with 1969 for second highest on record. Five of those reached major hurricane status of Category 3 or higher.

"Sit down please, you have not listened. That one is accumulated intensity of hurricanes making landfall in the US"

Believe me, I'm not standing. As you seem to not recognize it, you picked only hurricanes (ignoring tropical storms) and only US landfalls; by comparison to that cherry pittance, the Atlantic basin looms large.

"My scatterplot above ... is meaningful indeed. "

If, by 'meaning,' you find some hidden significance in a shotgun spread of data points. See #24 for the way you described it.

The ACE statistic is a wind speed-time duration metric. By focusing on this alone, you miss what is suggested here.

These storms are doing more damage because of they are associated with heavy 'predecessor rain events' (PREs), as tropical moisture is pulled along the storm track, as reported by Galarneau et al 2010:

PREs are coherent mesoscale regions of heavy rainfall, ... that can occur approximately 1000 km poleward of recurving tropical cyclones (TCs). PREs occur most commonly in August and September, and approximately 36 h prior to the arrival of the main rain shield associated with the TC. ... PREs are high-impact weather events that can often result in significant inland flooding, either from the PRE itself or from the subsequent arrival of the main rain shield associated with the TC that falls onto soils already saturated by the PRE.

A more comprehensive and sobering picture of storm effects is given in an unpublished piece by Drews 2007, who presents a breakdown of the ACE index into the components illustrated below.

As I said twice now, perhaps we can agree that this question remains open. It is tedious in the extreme to be overly dogmatic when it is clear that a better metric is needed.

Your scatterplot is rather meaningless - for complex emergent phenomena like hurricanes, a simple univeriate analysis like your scatterplot is meaningless in the extreme, as hurricanes are complex and multidimensional entities, from an analytic perspective.

Why no trend? Because Maue lumped all cyclones together and would have come up with something very different if he looked at just category 4, 5 storms? (is such a chart available?)
And if one does that, what about being charged with cherry picking?

I think the problem may be that ACE blends wind speed and storm duration, as seen here in Bell et al 2000:

... accumulating Vmax^2 for all 6-hourly periods in which the system is either a tropical storm or hurricane, thereby also accounting for the number and duration of storms while at a tropical storm status. This modified HDP index is referred to as accumulated cyclone energy (ACE) index, and is both a physically and statistically reasonable measure of overall activity during a given hurricane season.

This was a modification of 'hurricane destructive potential (HDP),' which was originated by William Gray in 1987.

The rate of energy release for each mm/hour of rainfall is three times as great as the solar energy (~350 Watts/m2) that falls on the same surface area. Thus the precipitation process concentrates heat that was used to evaporate moisture from large expanses of the tropics by factors of ten to a hundred into those regions where rain occurs. While solar heating of the atmosphere takes place mainly at the surface, the heat released by condensation occurs at high altitudes where it has a greater impact on the atmosphere's large scale circulation. Averaged over the entire Earth the heating released by precipitation is about five times greater than that produced by variations in surface heating.

Some people are still stuck in hypothesis testing mode, which I think is starting to get a little bit crazy. We can only test hypotheses that way. We cannot use that approach to establish that changing the radiative properties of the atmosphere is safe.

My claim is that we need to get our thinking out of nudge-world. This is not a nudge. ... I don't understand why people don't anticipate some ringing in a system that gets kicked this hard.

@DB, thanks!
(Note to web editor: Perhaps an index listing often quoted papers would be helpful, My attempts to search for information on this here weren't exactly fruitful).
@CBDunkerson the first paper, for instance, is being used to argue that there has been no increase/change in weather severity. Presumably it's been taken out of context; I'm looking for some context.

Looks like DB came to conclusions similar to what I posted above after skimming the two papers. With the background on what is being claimed it seems like 'skeptics' are just taking random papers on hurricanes and grossly misrepresenting what they say. Either that or they're really bad at reading comprehension.

Regarding observations, SREX differs significantly from IPCC AR4, and says (page 160):Based on research subsequent to the AR4 and Kunkel et al. (2008), which further elucidated the scope of uncertainties in the historical tropical cyclone data,
the most recent assessment by the World Meteorological Organization (WMO) Expert Team on Climate Change Impacts on Tropical Cyclones (Knutson et al., 2010) concluded that it remains uncertain whether past changes in any tropical cyclone activity (frequency, intensity, rainfall)exceed the variability expected through natural causes, after accounting for changes over time in observing capabilities. The present assessment regarding observed trends in tropical cyclone activity is essentially identical to the WMO assessment (Knutson et al., 2010): there is low confidence that any observed long-term (i.e., 40 years or more) increases in tropical cyclone activity are robust, after accounting for past changes in observing capabilities.

Regarding possible changes in hurricane intensity, SREX notes that there is a correlation between SST and intensity which at first glance would imply that global warming would increase hurricane intensity.

But SREX then goes on to note However, there is a growing body of research suggesting that local potential intensity is controlled by the difference between local SST and spatially averaged SST in the tropics (Vecchi and Soden, 2007a; Xie et al., 2010; Ramsay and Sobel, 2011). Since increases in SST due to global warming are not expected to lead to continuously increasing SST gradients, this recent
research suggests that increasing SST due to global warming, by itself, does not yet have a fully understood physical link to increasingly strong
tropical cyclones.

(crude translation .... both warm water and a temperature differential is needed to form and intensify hurricanes, and global warming does not necessarily increase differentials)

"The background to these enquiries stems from a simple observation: extra heat in the air or the oceans is a form of energy, and storms are driven by such energy. What we do not know is whether we might see more storms as a result of extra energy or, as other researchers believe, the storms may grow more intense, but the number might actually diminish."

That sounds plausible, but it is wrong,as should be clear to anyone familiar with basic thermodynamics. A storm is a heat engine--it converts thermal energy into mechanical energy (in the form of winds). A heat engine that converts all the thermal energy it takes in to mechanical energy is what is known as a perpetual motion machine of the second kind. It is impossible because it violates the second law of thermodynamics (entropy), in contrast to a perpetual motion machine of the first kind, which violates the first law (energy conservation). The standard example would be a ship that needed no fuel, because it ran off the heat of the ocean.

Actual heat engines absorb thermal energy from a hot source, convert some into mechanical energy, and dump the rest into a colder sink. What determines the amount of mechanical energy they get is not the temperature of the source but the temperature difference between source and sink. So simply raising the temperature of sea and air doesn't make more energy available. You need some mechanism that raises the temperature difference.

Hence the argument you offer is wrong (whether the conclusion is wrong I don't know). Either you don't understand the relevant science or you are willing to misrepresent the science in order to provide a simple argument for your conclusion. Your site is supposed to be offering accurate scientific information--the fact that it makes an argument inconsistent with elementary thermodynamics is a reason not to trust other arguments it makes.

Sources of information that can be trusted on politically contentious issues are rare and valuable. I'll check back in a few days to see if you are still making the same argument. If you are, you are not such a source.

David Friedman The observation you are commenting on does not imply any sort of perpetual motion machine as the energy that drives the heat engine is ultimately provided externally by the sun. However global warming makes more of the Sun's energy available for the creation and intensification of storms. If the Earth were thermodynamically a closed system, then your argument would have some merit, but it isn't.

I would suggest that it is a good idea to refrain from suggeting that others don't understand the science, it is generally better to adopt some humilty and assume that it is you that is wrong, and ask for an explanation of why your objection is incorrect.

So, David, if a difference exists "normally," then adding more to one side of the equation wouldn't produce a greater difference? The vertical profile of GHE warming is not uniform. The lower troposphere is warming at a greater rate than the upper troposphere. According to your understanding, would that not create a greater temp difference?

That's a simplistic answer, but your response was simplistic. This is not a simple box model we're dealing with. Tropical convection doesn't occur absent of other large-scale forces (increased available water vapor, for example). I'm also thinking you didn't click on the "intermediate" tab above.